1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel, and more particularly, to an LCD panel, the thickness of which can be reduced, and a method for fabricating the same.
2. Discussion of the Related Art
Recently, various flat panel display devices have been widely utilized to replace cathode ray tubes because of their light weight and small volume. Examples of the flat panel displays usually include LCDs, field emission displays, plasma display panels, and light emitting displays.
The LCD utilizes an electric field to adjust light transmittance of liquid crystal, thereby displaying an image. The LCD typically includes an LCD panel having liquid crystal cells arranged in a matrix shape, and a driving circuit for driving the LCD panel. The LCD panel is provided with pixel electrodes and a common electrode, which apply electric fields to the liquid crystal cells, respectively.
In general, the pixel electrodes are formed on a lower substrate of the LCD panel and correspond to the respective liquid crystal cells, and the common electrode is formed on the entire surface of an upper substrate of the LCD panel. The pixel electrodes are electrically connected to thin film transistors (TFTs) serving as switching elements. The TFTs supply data signals, by which the pixel electrodes together with the common electrode drive the liquid crystal cells.
FIG. 1 is a sectional view schematically illustrating an LCD panel according to the related art. As shown in FIG. 1, the related art LCD panel includes a color filter array substrate 4, a TFT array substrate 2, an upper polarization plate 160a attached to a front surface of the color filter array substrate 4, and a lower polarization plate 60b attached to a rear surface of the TFT array substrate 2. The color filter array substrate 4 is formed by sequentially depositing an upper substrate 42, a black matrix layer 44, a color filter layer 46, an overcoat layer 47, a common electrode 48, and an upper orientation film 50a. The TFT array substrate 2 further includes a lower substrate 1, TFTs, pixel electrodes 22 and a lower orientation film 50b formed on the lower substrate 1, liquid crystal 52 injected into a space between the color filter array substrate 4 and the TFT array substrate 2.
Each of the TFTs includes a gate electrode 6 connected to a gate line (not shown), a source electrode 8 connected to a data line (not shown), and a drain electrode 10 connected to corresponding one of the pixel electrodes 22 through a drain contact hole 26. Moreover, each of the TFTs further includes semiconductor layers 14 and 16 for forming a communication channel between the source electrode 8 and the drain electrode 10 by a gate voltage supplied to the gate electrode 6. The TFTs supply data signals from the data lines to the pixel electrodes 22 in response to gate signals from the gate lines.
The pixel electrodes 22 are located at pixel regions and are formed of a transparent conductive material with a high light transmittance. The pixel regions are divided from each other by the data lines and the gate lines interposing a gate insulating layer 12 therebetween. The pixel electrodes 22 are formed on a passivation film 18 formed on the front surface of the lower substrate 1, and are electrically connected to the drain electrodes 10 through the drain contact holes 26 formed through the passivation film 18. Moreover, the pixel electrodes 22 and the common electrode 48 generate a difference of electric potentials according to the data signals supplied from the TFTs. Due to the difference of electric potentials, the liquid crystal 52 located between the lower substrate 1 and the upper substrate 42 is rotated by isotropy of dielectric constants. The amount of light transmitted from a light source to the upper substrate 42 via the pixel electrodes 22 is adjusted by the rotated liquid crystal 52.
The black matrix layer 44 on the color filter array substrate 4 overlaps with TFT regions and the gate and data lines (not shown) of the lower substrate 1, and divides the pixel regions. The black matrix layer 44 serves to prevent light from leaking and to absorb external light, thereby increasing contrast. The color filter layer 46 is formed on the pixel regions, which are divided by the black matrix layer 44. The color filter layer 46 is differently formed according to Red (R), Green (G), and Blue (B) colors, thereby forming R, G, and B colors. The overcoat layer 47 is formed by applying a transparent resin having an insulating property on the upper substrate 42 including the color filter layer 46. The overcoat layer 47 serves to electrically insulate the black matrix layer 44, to which a designated voltage is applied, and the common electrode 48, to which a common voltage is applied, from each other.
In a TN mode LCD, the overcoat layer 47 is not utilized. In the event that the common voltage, serving as a reference when the liquid crystal 52 is driven, is applied to the common electrode 48, the common electrode 48 generates a difference of electric potentials with the pixel electrodes 22 formed on the lower substrate 1. In an IPS mode LCD, the common electrode is formed on the lower substrate 1.
The upper and lower orientation films 50a and 50b serve to orient the liquid crystal 52, and are respectively formed on the color filter array substrate 4 and the TFT array substrate 2 by applying an orienting material such as polyimide (PI), and performing a rubbing process. The lower polarization plate 60b is attached to the rear surface of the lower substrate 1 to polarize rays incident from a back light unit (not shown). The upper polarization plate 60a is attached to the front surface of the upper substrate 42 to polarize rays emitted from the LCD panel.
Each of the upper and lower polarization plates 60a and 60b is formed such that first and second passivation layers are stacked under the condition that a polarizer (not shown) is formed between the first and second passivation layers. Here, the polarizer is formed by stretching a Poly Vinyl Alcohol film and soaking the film in an iodine solution and a dye solution having a color differing from that of the iodine so that iodine molecules are arranged in parallel with the stretched direction. The first and second passivation layers are made of triacetate cellulose (TAC), and serve to prevent the stretched polarizer from being constricted and to protect the polarizer. Thus, the upper and lower polarization plates 60a and 60b are respectively attached to the rear and front surfaces of the bonded lower and upper substrates 1 and 42 by a polarization plate attaching process.
However, the related art LCD panel has several problems due to the polarization plate attaching process. First, there are foreign substances introduced into spaces between the LCD panel and the polarization plates 60a and 60b during the polarization plate attaching process, thereby generating defects in the LCD panel. Second, the polarization plates 60a and 60b attached to the LCD panel during the polarization plate attaching process generate scratches in the LCD panel. Third, the polarization plates 60a and 60b attached to the front and rear surfaces 1 and 42 of the LCD panel for polarizing rays are expensive, thereby increasing the production costs and thickness of the LCD panel.